1. Field of the Invention
The invention relates generally to a photo mask and a method of manufacturing the same, and a method of forming a photosensitive film pattern using the photo mask. More particularly, the invention relates to a photo mask and a method of manufacturing the same, and a method of forming a photosensitive film pattern using the photo mask, in such a manner that target photo mask pattern and photosensitive film patterns can be formed more accurately by changing a photo mask pattern.
2. Description of the Prior Art
In the manufacture process of semiconductor devices, the contact holes or various patterns are usually formed, through the photolithography process. The procedure of the photolithography process is as follows, as well known in the art. A photosensitive film pattern is formed through application of a photosensitive film and exposure and development of the photosensitive film using a photo mask, and an etch process is then performed using the photosensitive film pattern as a mask to form a target pattern. In this case, a non-transparent chrome pattern formed in the transparent substrate such as a quartz substrate, etc. is generally used as the photo mask (i.e., reticle).
FIG. 1A is a layout diagram of a conventional photo mask in which a capacitor of a DRAM (dynamic random access memory) device will be formed, FIG. 1B is a SEM (scanning electron microscope) photography of a photosensitive film pattern formed on a substrate using the mask in FIG. 1A, and FIG. 1C is a layout diagram of the photosensitive film pattern simulated using the mask in FIG. 1A.
Referring to FIG. 1A˜FIG. 1C, the photosensitive film pattern formed on the wafer by the mentioned photolithography process is distorted, compared to the shape of the design. In other words, in order to make the capacitor pattern of a rectangular shape, the photo mask pattern is designed to have the rectangular shape as shown in FIG. 1A. If the exposure and development processes are performed using the mask pattern, the photosensitive film pattern of an elliptical shape, not the rectangular shape, is formed on the wafer as shown in FIG. 1B.
This distortion is caused by an optical proximity effect that light passing the photo mask pattern causes interference between neighboring patterns in the photolithography process. There is a trend that distortion owing to the optical proximity effect becomes more important, as the size of the pattern to be resolved is smaller than the wavelength of the light source.
Due to this cause, there is a problem the critical dimension of the capacitor pattern formed on the wafer becomes smaller than the critical dimension of a desired pattern. Especially, in case of a long side axis direction in the elliptical circle, the critical dimension of the capacitor pattern is significantly reduced than a target critical dimension as shown FIG. 1C.
In order to solve the above problems, an optical proximity effect correction (hereinafter called ‘OPC’) method in which the length of the long side axis is in advance lengthened so that a desired size of the long side axis can be formed and an assistant pattern of an adequate shape is added, has been developed.
FIG. 2A is a layout diagram of the conventional photo mask pattern in which the capacitor to which OPC is applied will be formed, FIG. 2B is a SEM photography of the photosensitive film pattern formed on a wafer using the mask in FIG. 2A, and FIG. 2C is a layout diagram of the photosensitive film pattern simulated using the mask in FIG. 2A.
Referring to FIG. 2A˜FIG. 2C, in case of designing the mask pattern for photo, the photo mask pattern is formed using the OPC method wherein the size of the long side axis is lengthened and the assistant pattern is added in the long side axis direction. Next, the exposure and development process as shown in FIG. 2B forms the photosensitive film pattern in which the capacitor will be formed on the wafer. Thereby, the problem that the long side axis is reduced is solved by some degree (compare FIG. 1B and FIG. 1C, and FIG. 2B and FIG. 2C).
Though the reduction of the long side axis is reduced is solved by some degree using the mentioned technology, the same OPC patterns could not be exactly implemented on the photo mask. (By lengthening the length of the long side axis and adding an assistant pattern of an adequate shape). In other words, there is a problem that a uniform photo mask pattern could not be formed as the size of the assistant pattern becomes smaller than the resolution limit of the lighting equipment used when the photo mask pattern is fabricated using the OPC method since the design rule is reduced. Due to this, not only the regularity with the pattern formed on the photo mask is lowered but also the pattern is patterned in asymmetric shape right and left on the single pattern.
In addition, examining the photosensitive film pattern formed by the photography process using the photo mask (i.e., reticle), a phenomenon that the photosensitive film pattern is distorted is compensated for by some degree. However, the regularity between the photosensitive film patterns is lowered. Thereby, there is a problem that the characteristic of the semiconductor device is degraded since the regularity between the devices formed using the above photosensitive film pattern is lowered.